1. The Field of the Invention
The invention generally relates to multiplexed communication in fiber optic networks. More specifically, the invention relates to methods and apparatus for implementing a network using an optical add/drop module integrated in a patch cord device.
2. Description of the Related Art
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates or in other words, very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper conductor. Many conventional electrical networks are being upgraded to optical networks to take advantage of the increased speed and efficiency.
One goal of optical fiber networks is to maximize the amount of data traffic that can be transmitted along a single optical fiber. One way of increasing the amount of data traffic is by using various types of multiplexing arrangements. One such multiplexing arrangement is based on sending multiple signals through the same optical fiber using modulated carrier beams, each having a different frequency or wavelength than the other carrier beams. For instance, in one implementation known as coarse wavelength division multiplexing (CWDM), signals are sent using lasers with wavelengths varying between 1470 nm and 1610 nm in 20 nm increments. Each incremental wavelength represents a different data channel.
To accomplish a multiplexing implementation such as the one described above, several specialized data handling components are needed. One such component is an optical add/drop module, sometimes referred to as an OADM. An OADM extracts, or drops, a single channel from a multiplexed signal and provides the single channel to a network device that uses the channel. The network device utilizes the data, for example, carried by the dropped channel. In addition, a channel having the same wavelength as the dropped channel is added to the multiplexed optical signal using the OADM. The added channel may have the same or different data compared to the dropped channel. The multiplexed optical signal is then further propagated on the optical network after the drop and add operations have been performed.
A typical example of a common OADM is shown in FIG. 1. The optical add drop module (OADM) 100 has four ports, including an input port 102, a drop port 104, an add port 106 and an output port 108. The external interface to the port is generally configured using an industry standard connector, such as small form factor pluggable module. Interface cords with connectors configured to mate with the connectors on the OADM module 100 are used to connect the OADM module 100 to an optical network and to other components existing on the optical network.
In one example, the OADM module 100 is connected to a communications panel 112 through an input interface cord 110. The communications panel 112 is in optical communication with the fiber optic network and transmits a multiplexed signal to the input interface cord 110. The input interface cord 110 is also connected to the module input connector 102. Internally, the module includes optical components that separate a single channel from the multiplexed signal. A drop interface cord 114 is connected to the drop port 104. The drop interface cord 114 is also connected to a network device 116, which may be a client computer or other device having need of data carried on channels from the multiplexed signal. The separated, or dropped, channel is supplied to the network device 116 through the drop interface cord 114. The network device 116 extracts the appropriate data from the dropped signal and returns, or adds, the dropped signal to the OADM module 100 through an add interface cord 118. The add interface cord 118 is coupled to the OADM module 100 via the add port connector 106.
Internal to the OADM module 100, the dropped signal is added to the multiplexed signal and transmitted via the output port 108 to the output interface cord 120. The output interface cord 120 is coupled to a communications panel 122, which may be the same communications panel 112 previously mentioned or a different communications panel. In either case, the communications panel 122 is coupled to the optical network and is configured to provide multiplexed signals to network devices. The OADM module 100 is usually mounted in a rack.
Typically the OADMs used in conventional optical networks are implemented using a physical infrastructure that is often bulky. For example, many OADMs are rack mounted in a case or a chassis. Thus, many optical networks only have a limited number of physical locations that are available for OADMs, namely those that can accommodate the physical size of the module. Another disadvantage of OADMs is that they typically involve the use of a relatively large number of connectors and associated cords, as described above in reference to FIG. 1, which also require significant physical space and manipulation.